When most people think of fast food, images of burgers and fries come to mind. But if you are part of the Slow Food Movement, even sliced bread would be in the picture. Although all convenience foods do not come loaded with calories, recent studies have me thinking the faster we get our food, the easier it is to get fat.

Let me explain.

For most of human history, hunting and gathering food took all of our time and energy. When we figured out how to raise crops and animals more than 10,000 years ago, we had a somewhat more reliable food supply, but still had to work very hard to get something to eat. Then with the dawn of modern agriculture less than 200 years ago, the era of cheap, easy and fast food began.

Whether it’s take-out fried chicken or boneless, skinless chicken cutlets, fast food brought with it a dramatic change in our way of life. Once we no longer had to expend much effort to get our food, we had a lot more time to think about other things, like ways to produce even more food even faster.

But what if the evolutionary connection between food and work is important to our survival? It appears this may be true for some animals.

Researchers at Johns Hopkins University found that the more effort mice had to expend to get their food, the more they valued it. In the study, mice were trained to press levers to receive treats. They preferred the sugary treat that took 15 presses of the lever over the treat they could get after pressing the lever just once. Then when the sugary treat was replaced with a low calorie (less tasty) snack, the mice continued to show a preference for the harder to get treat.

The study suggests that mice valued working for their foods so much they would eat something less palatable (and better for them) as long as they could “earn it” through hard work.

A related finding was seen in birds. Researchers from the Evolutionary Biology Centre in Upsala, Sweden found that survival among birds in urban areas was based on brain size because they have to work harder to find food than birds living in the countryside. These “urban adapters” as the researchers called them, are able to develop novel foraging techniques and sustain a varied diet, which is key to survival in a changing environment. Again, working for food paid off.

I realize animal studies cannot explain human behavior. But it makes me think our quick and easy food supply may be bad for us in more ways than just nutritionally. I know I have never heard anyone complain about a meal of home-grown, home-made food, have you?